Method of making an aerofoil-shaped blade or blade blank

ABSTRACT

A method of making an aerofoil-shaped blade or blade blank comprises forming two blade halves which are assembled together to form the complete blade or blade blank. The surfaces of adjacent blade halves have cooling fluid passages therebetween, and in assembling the blade halves a sheet of brazing material is interposed between the blade halves. The sheet is provided with slots therein which are aligned with and of corresponding shape to the cooling fluid passages.

United States Patent Jones [5 METHOD OF MAKING AN AEROFOIL- SHAPED BLADEOR BLADE BLANK [72] Inventor: John Windsor Jones, Thornton-in-Craven,

Skipton, England Rolls-Royce Limited, Derby, Derbyshire, England 221Filed: Mar. 17, 1969 211 Appl.No.: 807,586

[73] Assignee:

[58] Field of Search ..29/156.8 H, 156.8 B, 156.8 R, 29/1568 T; 416/213[56] Reierences Cited UNITED STATES PATENTS 2,807,437 9/1957 Roush..29/156.8 X

[451 Apr. 18, 1972 2,821,495 1/1958 Dulin ..29/487 X 3,025,596 3/ 1962Ward et a1 ..29/501 X 3,083,451 4/1963 Atkinson ..29/501 X 3,088,1925/1963 Turner ..29/156.8 3,110,102 11/1963 Pfefferkom... ..29/4903,170,234 2/1965 Tarr ..29/498 X 3,197,858 8/1965 Feduska et al.....29/498 X 3,329,596 7/1967 Abt et a1. 29/1568 X 3,342,971 9/1967Kaarlela ..29/487 X 3,349,465 10/1967 La Fan et a1 ..29/ 157 3 PrimaryExaminer-Charlie T. Moon Assistant Examiner-Donald P. RooneyAttorney-Cushman, Darby & Cushman [57] ABSTRACT A method of making anaerofoil-shaped blade or blade blank comprises forming two blade halveswhich are assembled together to form the complete blade or blade blank.The surfaces of adjacent blade halves have cooling fluid passagestherebetween, and in assembling the blade halves a sheet of brazingmaterial is interposed between the blade halves. The sheet is providedwith slots therein which are aligned with and of corresponding shape tothe cooling fluid passages.

7 Claims, 4 Drawing Figures PATENTEDAPR 181912 3, 656,222

lnvenlor A ttorneys METHOD OF MAKING AN AEROFOIL-SHAPED BLADE OR BLADEBLANK This invention concerns a method of making an aerofoilshaped blade(or blade blank) from which an aerofoil-shaped blade is to be formed,such, for example, as a rotor blade of a high pressure turbine rotor ofa gas turbine engine.

The object of the invention is to provide an inexpensive andsatisfactory method of forming such a blade or blade blank with acooling air passage or passages.

According to the present invention, there is provided a I method ofmaking an aerofoilshaped blade comprising forming a plurality of bladeportions which may be assembled together to form the complete blade, atleast one of the surfaces of adjacent portions being formed to provideat least one cooling fluid passage between the portions, assembling thesaid blade portions together with a sheet of brazing material interposedbetween the or each adjacent pair of blade portions, at least one slotbeing provided in said at least one sheet said at least one slot beingaligned with, and of corresponding shape to, the respective coolingfluid passage, the brazing material of said at least one sheet beingadapted to form a diffusion braze with the material of the bladeportions, and heat treating the assembly of blade portions and brazingmaterial so that the blade portions are diffusion brazed to each other.

The or each cooling fluid passage is preferably formed by electroforming(e.g. by spark machining) a groove in at least one of the surfaces ofthe adjacent blade portions.

The surfaces of adjacent blade portions are preferably formed to preventrelative angular movement therebetween.

The or each said slot may be formed after the respective sheet has beenpositioned with respect to one of the respective blade portions.

The brazing material preferably comprises a mixture of an alloy and of asynthetic resin material, the synthetic resin material being such as tobecome vaporized, and thus removed, during the heat treatment.

The heat treatment preferably is a solution heat treatment whichincludes heating said assembly in vacuo until the brazing materialmelts.

. Prior to the heat treatment, the or each cooling fluid passage may becoated with a coating material which prevents the adhesion of brazingmaterial thereto.

. The invention also comprises an aerofoil-shaped blade or blade blankwhen made by the method set forth above.

The invention is illustrated, merely by way of example, in theaccompanying drawings, in which:

FIG. 1 is a diagrammatic perspective view of a blade blank formed in twoportions,

FIG. 2 is a diagrammatic plan view of the blank of FIG. 1, looking inthe direction of the arrow 2 of FIG. 1,

FIG. 3 is a view similar to FIG. 2 but showing the two portions of theblank separated, and

FIG. 4 is a diagrammatic view of one of the said portions looking in thedirection of the arrow 4 of FIG. 3.

In FIG. 1 there is shown a blade blank from which may be formed anaerofoil-shaped blade 11 which is indicated by dotted lines in FIG. 2,the blade 11, being for example, a turbine rotor blade of a highpressure turbine of a gas turbine eng The blade blank 10 is formed oftwo portions 12, 13 which are respectively provided with adjacentinter-fitting surfaces l4, 15, which are respectively concave andconvex.

As indicated in FIG. 3, the surfaces 14, 15, are not truly cylindricalin shape and are thus prevented from having relative angular movementwith respect to each other. For example, the surface 14 has a portion 16which is truly cylindrical and has a radius of curvature r, the portion16, however, merg ing smoothly into a flat portion 17 which istangential thereto. The portion 17 is disposed at an angle (b (e.g. of60) to the normal 18 to the sides of the blade blank 10.

As will be appreciated, the blade portions 12, 13 may, if desired, beformed with a centrallydisposed cylindrical portion 16 and with flattangential portions 17 on each of the opposite sides thereof.

The surfaces 15 is of course correspondingly formed.

As indicated, in FIG. 4, the surface 14 is formed with cooling airgrooves 20, 21, 22, and similar cooling air grooves, which are alignedtherewith, may, if desired, be provided in the surface 15. The surface14 and the cooling air grooves 20- 22 therein are electro-formed in therespective blade portion, e.g. by spark machining. The electrodeemployed for such spark machining may, for example, itself be producedby the method disclosed in our co-pending British Pat. application No.13580/68.

The blade portion 13 may be manufactured from a bar (not shown) byturning the bar and splitting it prior to the formation of the coolingair passages (if any) therein. The blade portion 12 may be forged priorto the said spark machining, and the surface 14 may be finish ground,e.g. by means of electrolytic grinding using a graphite wheel.

The blade portions 12, 13 are then de-greased and are brazed together byassembling them to form the complete blade blank 10, a sheet 23 ofbrazing material being interposed between the surfaces 14, 15 of theblade portions l2, 13.

The brazing material of the sheet 23 may comprise a mixture of an alloyand of a synthetic resin material, the latter being such as to becomevaporized and thus removed during the solution heat treatment referredto below. The brazing material moreover is such as to be compatible withand adapted to form a diffusion braze with the material of the bladeportions 12, 13. Thus, if, for example, the blade portions 12, 13 areformed of a nickel based alloy such as Nimonic or Nimonic 118, (Nimonicbeing a Registered Trade Mark), the brazing material of the sheet 23 mayconsist of 60 percent by weight of an alloy sold under the Trade NameNICROBRAZE 4775" and 40 percent by weight of an acrylic resin. Forexample, the sheet 23 may be produced by forming sintered buttons of themixture of alloy and acrylic resin, and then forming the sheet 23 bypressing these buttons between heated palates.

Having been so formed, the sheet 23 is attached to the blade portion 13e.g. by means of a cement sold under the Trade Name TENSOL No. 6 andslots (not shown) are formed in the sheet 23 after it had been sopositioned with respect to the blade portion 13, the said slots being ofcorresponding shape to, and being aligned with, the grooves 20-22. Thecutting of the slots may be effected by using a small air turbine drillfollowing the profile of the grooves 20-22.

The blade portions 12, 13, with the sheet 23 therebetween, are thenplaced together in a jig (not shown). The jig is, however, providedmerely in order to locate the blade portions l2, 13 with respect to eachother, no gripping or positive pressure being applied to urge the bladeportions 12, 13 together. Thus in the solution heat treatment referredto below, during which the blade portion 12 will be disposed: above theblade portion 13, no force is employed to effect such urging other thanthat of gravity, whereby there will be little tendency for the brazingmaterial to be squeezed out of position.

The solution heat treatment comprises placing the assembly in an ovenwhich is maintained at an elevated temperature until the brazingmaterial melts. The solution heat treatment is effected in vacuo, theheating and vacuum conditions effecting removal of the acrylic binder ofthe sheet 23, with the result that the blade portion 12 moves undergravity towards the blade portion 13.

Thus, for example, if the blade portions 12, 13 are formed of Nimonic105 the assembly of the blade portions 12, 13 and sheet 23 is given asolution heat treatment for 4 hours at 1,l50 C, and then a furthertreatment of 16 hours at l050 C, while if the blade portions 12, 13 areformed of Nimonic l 18, the solution treatment is for 1 /2 hours at1,190 C, the assembly is allowed to cool from the temperature of 1,190C, to 1,000 C, and is thereafter rapidly cooled to room temperature.

Prior to the said solution heat treatment, each of the grooves 20, 22may be coated with a coating material which prevents the adhesion ofbrazing material thereto. Thus the coating material may for example beconstituted by a thin film of the material sold under the Trade NameNICROBRAZE GREEN Stop-off paint which is basically a suspension ofchromic oxide in an organic carrier. During brazing, this paint becomescharred so as to give a black dust over which the brazing alloy will notflow.

At the end of the heat treatment the assembly of portions 12, 13 willhave become diffusion brazed to each other. A two-part blade blank isthus formed, the joint between which, at the blade operatingtemperature, is as strong as that of the parent metal so that there isno danger of the joint melting at a relatively low temperature. Fromthis blade blank the finished blade 11 may thereafter be formed by anysuitable method.

Iclaim:

1. In a method of making an aerofoil-shaped blade comprising forming aplurality of blade portions which may be assembled together to form thecomplete blade, at least one of the surfaces of adjacent portions beingformed to provide at least one cooling fluid passage between theportions assembling the said blade portions together with a sheet ofbrazing material interposed between the or each adjacent pair of bladeportions, at least one slot being provided in said at least one sheet,said at least one slot being aligned with, and of corresponding shapeto, the respective cooling fluid passage, the brazing material of saidat least one sheet being adapted to form a diffusion braze with thematerial of the blade portions, and subjecting the assembly of bladeportions and brazing material to elevated temperatures by first brazingthe blade portions to each other and thereafter heat treating theassembly, the improvement wherein said brazing and solution heattreatment are carried out in one continuous operation such that at theend of the treatment at elevated temperatures the blade portions becomediffusion brazed to each other and the joint between the two bladeportions is as strong as the parent metal, thereby avoiding a jointmelting at a relatively low temperature.

2. A method as claimed in claim 1 in which said at least one coolingfluid passage is formed by electroforming a groove in at least one ofthe surfaces of the adjacent blade portions.

3. A method as claimed in claim 1 in which the surfaces of adjacentblade portions are formed to prevent relative angular movementtherebetween.

4. A method as claimed in claim 1 in which said at least one slot isformed after the respective sheet has been positioned with respect toone of the respective blade portions.

5. A method as claimed in claim 1 in which the brazing materialcomprises a mixture of an alloy and of a synthetic resin material, thesynthetic resin material being such as to become vaporised, and thusremoved, during the heat treatment.

6. A method as claimed in claim 1 in which the heat treatment is asolution heat treatment which includes heating said assembly in vacuountil the brazing material melts.

7. A method as claimed in claim 1 in which, prior to the heat treatment,the or each cooling fluid passage is coated with a coating materialwhich prevents the adhesion of brazing material thereto.

1. In a method of making an aerofoil-shaped blade comprising forming aplurality of blade portions which may be assembled together to form thecomplete blade, at least one of the surfaces of adjacent portions beingformed to provide at least one cooling fluid passage between theportions assembling the said blade portions together with a sheet ofbrazing material interposed between the or each adjacent pair of bladeportions, at least one slot being provided in said at least one sheet,said at least one slot being aligned with, and of corresponding shapeto, the respective cooling fluid passage, the brazing material of saidat least one sheet being adapted to form a diffusion braze with thematerial of the blade portions, and subjecting the assembly of bladeportions and brazing material to elevated temperatures by first brazingthe blade portions to each other and thereafter heat treating theassembly, the improvement wherein said brazing and solution heattreatment are carried out in one continuous operation such that at theend of the treatment at elevated temperatures the blade portions becomediffusion brazed to each other and the joint between the two bladeportions is as strong as the parent metal, thereby avoiding a jointmelting at a relatively low temperature.
 2. A method as claimed in claim1 in which said at least one cooling fluid passage is formed byelectroforming a groove in at least one oF the surfaces of the adjacentblade portions.
 3. A method as claimed in claim 1 in which the surfacesof adjacent blade portions are formed to prevent relative angularmovement therebetween.
 4. A method as claimed in claim 1 in which saidat least one slot is formed after the respective sheet has beenpositioned with respect to one of the respective blade portions.
 5. Amethod as claimed in claim 1 in which the brazing material comprises amixture of an alloy and of a synthetic resin material, the syntheticresin material being such as to become vaporised, and thus removed,during the heat treatment.
 6. A method as claimed in claim 1 in whichthe heat treatment is a solution heat treatment which includes heatingsaid assembly in vacuo until the brazing material melts.
 7. A method asclaimed in claim 1 in which, prior to the heat treatment, the or eachcooling fluid passage is coated with a coating material which preventsthe adhesion of brazing material thereto.